1、32點陣圖資料轉換成24位點陣圖資料：

unsigned char* RGB32TO24(unsigned char* src, int width, int height)
{
	uint8_t* data = NULL;
	uint32_t src_row_bytes;
	uint32_t dst_row_bytes;
	uint32_t off;
	int i,j;
	uint32_t* ptr;
	uint8_t* img;
	uint32_t color;
	int pad;
	
	src_row_bytes = width << 2;
	dst_row_bytes = (width * 3 + 3) & ~3;
	pad = dst_row_bytes - width * 3;

	data = (uint8_t*)malloc(dst_row_bytes * height);
	if (!data)
	{
		return NULL;
	}
    
	off = (height - 1) * dst_row_bytes;
	ptr = (uint32_t*)src;
	
	for(i = 0; i < height; i++)
	{  
		img = data + off;
		for (j = 0; j < width; j++)
		{   
			color = *ptr++;
			*img++ =  color & 0x000000FF;
			*img++ =  (color >> 8) & 0x000000FF;
			*img++ =  (color >> 16) & 0x000000FF;
		}
		off -= dst_row_bytes;
	}
	return data;
}
 

src_row_bytes為32位點陣圖一行所佔的記憶體空間大小，一個畫素佔據4個位元組的資料，所以不用考慮記憶體對齊問題；dst_row_bytes為24位點陣圖一行所佔據記憶體空間，一個畫素3個位元組，所以這裡需要考慮記憶體位元組對齊問題，dst_row_bytes需要是容納width*3的最小的4的倍數。

2、24位點陣圖轉換成32位點陣圖：

unsigned char* RGB24TO32(unsigned char* src, int width, int height)
{
	uint8_t* data;
	int row_bytes;
	int i,j;
	uint8_t* dst;
	uint8_t* ptr;
	int src_pad;
	uint32_t off;

	row_bytes = (width * 3 + 3) & ~3; 
	data = (uint8_t*)malloc(width * 4 * height);
	if(!data)
		return NULL;
	off = (height - 1)*row_bytes;
	dst = data;
	for(i = 0; i < height;i++)
	{   
        ptr = src + off;
		for(j = 0; j < width; j++)
		{
			*dst++ = *ptr++;
			*dst++ = *ptr++;
			*dst++ = *ptr++;
			*dst++ = 0;
		}
        off -= row_bytes;
	}
	return data;
}
 

row_bytes跟上文一樣，不贅述。